[petsc-dev] Lagging the numerical factorization for one of the fields of fieldsplit preconditioner

[Jed Brown]

On Tue, Mar 15, 2011 at 23:28, Barry Smith <bsmith at mcs.anl.gov> wrote:

> I'd like the flow control and ability to "do things" on inner blocks to be
> the same regardless of the matrix class being used.  I don't want suddenly
> much more to code with or better functionality if you've chose one matrix
> class over another (maybe much better speed but that is a different
> question).  So that's why I don't want it hardwired to MatNest


It's not a matter of hardwiring it to MatNest, rather making the Mat that
comes out of MatGetSubMatrix() hold information about whether it has been
modified. If you use AIJ, then you have necessarily reassembled the entire
thing even though part of it might be constant. It sounds like you're asking
for an external way to promise solvers that part of a matrix didn't change.
I'd rather let the solver check whether the matrix changed according to an
existing established API and leave the Mat responsible for saying when
things change. Seems more robust and could be used in many other places (for
example, TS could always think of the problem as nonlinear transient, but
have operators that happen to be linear time-independent only be factored
once).

An inexact method where the matrix is changing, but you want to delay setup
anyway is a different matter and seems to need to go into the solver.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20110315/b2bc7ada/attachment.html>